There has been a long-recognized need to have a means to automatically maintain the air pressure in inflatable tires on motor vehicles to compensate for slow leakage and/or changes in the atmospheric environment; i.e., air temperature and pressure fluctuations. Existing products commonly found in the marketplace include Central Tire Inflation System, AIRGO Tire Maintenance System (TMS), Meritor Tire Inflation System (MTIS), PressureGuard system, and TIREMAAX system. Such tire-inflation systems detect when the air pressure in a particular tire has dropped and inflate that tire back to the proper level as long as there is only a minor air leak.
For example, the AIRGO Tire Maintenance System (TMS) is a “smart” system for tractor trailers that monitors tire pressure and inflates tires as necessary to keep pressure at the right level. It uses air from the trailer's brake-supply tank to inflate the tires.
The Meritor Tire Inflation System (MTIS) is also designed for use on tractor trailers. It uses compressed air from the trailer to inflate any tire that falls below its appropriate pressure. Air from the existing trailer air supply is routed to a control box and then into each axle. The air lines run through the axles to carry air through a rotary union assembly at the spindle end in order to distribute air to each tire. If there is significant air-pressure loss, then an indicator light informs the driver.
The PressureGuard system routes air from the trailer's air supply through the axles, then to the wheel hubs, and then to the tire valves.
The TIREMAAX system uses the trailer's air supply to maintain a specific level of tire inflation. When the system detects low pressure, it signals the operator/driver, and then directs air from the trailer air tank in the specific tire needing inflation.
While these available tire inflation systems vary in design, they share some common elements. This type of system uses air from the same compressor that supplies air to the brakes or from the trailer's brake supply tank to inflate the tires. The air lines run through the axles to carry air through a rotary union assembly at the spindle end in order to distribute air to each tire. However, due to very high complexity and high costs, the above listed tire inflation systems are made almost exclusively for large commercial vehicle, tractor trailers and military vehicles.
Other tire-inflation systems that are oriented toward the consumer market are the EnTire system, Cycloid AirPump system, Bridgestone Air Hub system, and The Pirelli Safety Wheel System.
The EnTire system uses a valve that allows intake of air from the atmosphere. The system then pumps the air into the under-inflated tire using a peristaltic-pump action, with the goal of maintaining a constant specific pressure in the tire.
The Cycloid AutoPump system has a small, wheel-hub-mounted pump that is powered by the turning of the wheels. Mounted on the wheel hub behind the center cap, the pump adds air through a check-valved tube that travels from the wheel hub to the tire cavity, and can add up to 2.5 psi per hour to an underinflated or leaking tire. In addition, the pump's self-contained electronics continuously monitor tire pressure, tire temperature (so it won't overpressure the tire), wheel rotations, and will send a signal to an internal receiving antenna if a large pressure loss (2 to 3 psi) is detected.
The Bridgestone Air Hub system (from Bridgestone Cycle of Japan) uses a rotating air pump that replenishes air in the tire as one pedals a bicycle. Like the EnTire system, it keeps the air in the tires at a constant pressure level. The air pump is located in the wheel hub and is run by rotating the wheel.
The Pirelli Safety wheel System uses a monitoring system along with a special rim and an internal tube containing compressed air. It also has a valve to regulate the pressure between the tube and the tire.
The main problem with these existing products is that the wheel-hub-mounted pump (peristaltic pump), which is powered by the turning of the wheels, requires substantial modification to the standard design of the wheel-hub and wheel assembly, as well as a special rim design for the wheel. Another problem with these existing tire-inflation systems is that the wheel and the compressor are designed to be an integral part of the vehicle and cannot be removed and reinstalled on another vehicle.
What is needed is a simple design for a small, individual-wheel-based air compressor/regulator for tire air pressure, which can be easily removably coupled to a wheel-and-tire assembly, as well as can be easily coupled to other similarly-sized wheel-and-tire assemblies.